1. Field of the Invention
This invention relates to the field of particle concentrators, and more particularly to an apparatus and method for capturing target chemical substances adherent to a substrate that has been rubbed on the surface of a test subject to test for the presence of the target chemical substances. Preconcentration of the target substances results from the rubbing (alternatively referred to herein as xe2x80x9cswipingxe2x80x9d) of the substrate on the test surface. Specifically, according to the invention, target substances thus preconcentrated are removed (or, as the term is used herein, xe2x80x9cevolvedxe2x80x9d) from the substrate by heating the substrate in the presence of suction or other gas flow associated with a chemical analyzer such as a portable ion mobility spectrometer. Heating is accomplished by passing current through the swiped substrate, which comprises metallic felt or another similar porous metallic material. For purposes of this disclosure, including the appended claims, xe2x80x9csuctionxe2x80x9d in association with the chemical analyzer is intended to include all modalities through which gases are caused to pass from outside of the anayzer to inside the analyzer, regardless of whether the fan or other means for causing the flow of gases into the analyzer resides inside the analyzer or external to it. The apparatus of the invention is suited to human portability and is especially useful in conjunction with detecting compounds such as explosives, illegal drugs, other controlled substances and chemical agents. For purposes of this application, in the context of describing the claimed invention, the term particle is intended not to exclude vapor.
2. Description of the Related Art
Additional background information, supplemental to the information provided here, is found in U.S. Pat. No. 5,854,431 xe2x80x9cParticle Preconcentratorxe2x80x9d and in pending U.S. patent application Ser. No. 09/339,349, both of which are incorporated by reference herein in their entirety.
The detection of explosives, narcotics or other chemicals is a growing part of contraband detection. Recent years have seen rapid development of detectors capable of identifying the presence of explosives by capturing and identifying either vapors emanating from explosive materials or particles of explosive material, or both. Similarly, such detectors can also identify vapors and particles associated with other forms of contraband such as illegal drugs and other controlled substances. Such vapors and particles associated with contraband may be present and detectable on or near persons or objects that have been exposed to contraband materials and substances. Suitable detectors for this purpose include, but are not limited to, ion mobility spectrometers (IMS), electron capture detectors, mass spectrometers (MS), and chemiluminescence-based systems.
Detection of explosives, narcotics or other contraband substances demands reliable and convenient means for collecting and analyzing sample. The ""431 patent and the pending application Ser. No. 09/339,349 mentioned above are examples of ways to collect trace amounts of target chemical in dilute concentration in gases. The present invention offers an alternative that relates to the use of the technique of rubbing or swiping a surface of an article being tested for the presence of target chemicals.
Swiping surfaces in order to concentrate sample is well known in the art of chemical detection. A challenge remains, though, in how to reliably analyze chemicals collected and concentrated using the swiping approach, especially so that analysis results can be obtained quickly in a field setting. The present invention offers a quick and reliable method and apparatus to capture the target chemicals collected using the swiping technique and to deliver those chemicals to an analyzer for detection. An important aspect of the invention is that heat is used in a controlled fashion to drive off chemicals adherent to the swiped substrate. For purposes of this disclosure, the term xe2x80x9cevolvexe2x80x9d is used in conjunction with the process whereby target chemicals are driven off of the substrate as a consequence of application of heat.
The method and apparatus of the present invention rely on the use of a porous metallic substrate as the material used for swiping test surfaces. This porous metallic substrate forms part of an electrical circuit though which current passes causing the substrate to heat up. As the substrate heats in this fashion, target chemicals evolve from the surface of the substrate in a controlled manner. The evolved chemicals are then carried directly into an analyzer such as an IMS. (Other suitable analyzers include, but are not limited to, electron capture detectors, mass spectrometers and chemiluminescence-based systems.)
The apparatus of the present invention includes a heating device that can be conveniently attached to the gas inlet of an IMS or other portable detector. In the preferred embodiment, the swiped metallic substrate is held in place over an aperture opening toward the gas inlet of a portable IMS. Each end of the substrate is secured between electrode surfaces of like charge so that one end of the substrate is clamped between two positive electrodes and the other end is clamped between two negative electrodes, with the portion of the substrate between the ends positioned over the aperture. When positive and negative charges are applied to the positive and negative electrodes, respectively, current passes through the substrate, causing it to heat due to electrical resistance. At the same time, a suction capability, such as a pump, in the IMS in activated. As target chemicals evolve from the surface of the swiped substrate, they are captured and carried into the IMS for detection.
The invention includes features such as a hinged box within which the electrical elements of the apparatus are housed for convenient positioning of the substrate. In the preferred embodiment, a hinged box is used so that in an open position the substrate can be easily inserted or removed, and in the closed position the substrate is secured in place by the pairs of electrodes described.
An object of the invention is to provide an apparatus for use in collecting chemical substances from a substantially planar porous metallic substrate.
Another object of the invention is to provide a method for collecting chemical substances adhering to a substantially planar porous metallic substrate.
Yet another object of the invention is to provide an apparatus comprising a first support member including an aperture, and affixed to the first support member, in a first position adjacent to the aperture, a first electrical contact adapted to receive electrical current so that the first electrical contact can attain a positive electrical charge, and affixed to the first support member, in a second position adjacent to the aperture different from the first position, a second electrical contact adapted to receive electrical current so that the second electrical contact can attain a negative electrical charge.
Yet another object of the invention is to provide an apparatus further comprising a second support member, and affixed to the second support member, a third electrical contact adapted to receive electrical current so that the third electrical contact can attain a positive electrical charge, and a fourth electrical contact adapted to receive electrical current so that the fourth electrical contact can attain a negative electrical charge, the third and fourth electrical contacts being positioned so that when the second support member is placed adjacent to the first support member, the first electrical contact can lie substantially adjacent to the third electrical contact, and the second electrical contact can lie substantially adjacent to the fourth electrical contact.
Yet another object of the invention is to provide an apparatus whereby when a substantially planar porous metallic substrate is placed across the aperture described above. The substrate can be held at one locus on the substrate between the first and third electrical contacts, and also at a different locus on the substrate between the second and fourth electrical contacts, thereby completing an electrical circuit wherein electrical current can pass through the substrate.
Another object of the invention is to provide a method for collecting target chemical substances comprising the steps of rubbing a substantially planar porous metallic substrate on an article to which at least one target chemical substance adheres, positioning the substrate so that a portion of the substrate lies across an aperture connected to a chemical analyzer including a suction capability, forming electrical contact between a first electrode and a first locus of the substantially planar porous metallic substrate,forming electrical contact between a second electrode and a second locus of the substantially planar porous metallic substrate, the second locus being different from the first locus, whereby when electrical potentials of opposite charge are applied to the first and second electrodes current can flow through the substrate between the first locus and the second locus, applying potentials of opposite charge to the first and second electrodes of sufficient magnitude to cause current to pass through the substrate and heat the substrate so that at least portion of the at least one target chemical substance evolves from the substrate, and activating the suction capability of the analyzer so that target chemical substance evolved from the substrate passes in to the analyzer and subjected to chemical analysis.
An advantage of the present invention is that it provides a convenient and reliable method and apparatus for collecting target chemicals adherent to a swiped substrate and delivering those target chemicals to a detector for analysis.
Other objects, advantages and novel features will become apparent to those skilled in the art upon examination of the following description or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.